Evaluation of key factors influencing urban ozone pollution in the Pearl River Delta and its atmospheric implications

In recent years, the concentration of ozone (O3) in typical urban agglomerations in China has generally increased. This study carried out a three-year observation in the active photochemical reaction period (August-November) in Shenzhen, a megacity in the Pearl River Delta (PRD). Principal coordinate analysis (PCoA) was first applied to identify the major factors influencing daily maximum 8-h average O3 (MDA8-O3) concentration. Then, the MDA8-O3 concentration fitting equation was established by a stepwise multiple linear regression (MLR). In result, sensitivity test based on the fitting equation showed that temperature (+35.8%), photolysis rate of j[NO2] (+11.1%), relative humidity (-10.4%) and photolysis rate of j[O1D] (-9.5%) had more effect on the concentration of MDA8-O3 with per factor perturbation (25% change), while increments of oCO (6.9%) and NO2 (2.7%) had less effect. The insignificant effect produced by NO2 is consistent with Shenzhen being in a transition area for O3-VOCs-NOx sensitivity. Moreover, it is found in this study that PM2.5 likely promotes O3 formation by scattering light to influence j[NO2] and j[O1D] differently, which provides a new explanation for the coupled formation of PM2.5 and O3 in the PRD region.